Influence of urea on microstructure and optical properties of YPO4:Eu3+ phosphors

YPO4:Eu3+ phosphors were synthesized by solution coprecipitation method assisted by urea in the precursor reaction solution. X-ray diffraction spectral analysis showed that the samples synthesized with urea had smaller particle size and lower crystallinity than those samples synthesized without urea. Moreover, the calculated strain result indicated that the Eu3+ site in the former exhibited a lower crystal field symmetry than that in the latter. Hence, the influence of crystal field symmetry dominated luminescence efficiency rather than crystallinity because the luminescence intensity observed in Eu0.05Y0.95PO4 synthesized with 1.0 g urea was six-fold higher than that of the as-synthesized sample. With increased concentration of Eu3+ ion, the luminescence intensity initially increased, and then subsequently decreased as the concentration of Eu3+ ion exceeded 12 mol.% due to concentration quenching. The optimal condition for YPO4:Eu3+ phosphor was Eu0.12Y0.88PO4 with 1.0 g urea added in the precursor. The luminescence intensity of the optimal condition was again enhanced 1.6-fold relative to that of Eu0.05Y0.95PO4 synthesized with 1.0 g urea.